Serine/threonine kinases are a member of the eukaryotic protein kinase superfamily. Enzymes of this class specifically phosphorylate serine or threonine residues of intracellular proteins and are important in mediating signal transduction in multicellular organisms. Many serine/threonine kinases occur as intracellular proteins which take part in signal transduction within the cell, including signal transduction to the nucleus and the activation of other proteins. Other serine/threonine kinases, such as G protein-coupled receptor kinases, are found in cell membranes and participate in transmembrane signalling.
As such, phosphorylation of serine or threonine by serine/threonine kinases is an important mechanism for regulating intracellular events in response to environmental changes. A wide variety of cellular events are regulated by serine/theronine kinases. A few examples include the ability of cells to enter and/or complete mitosis, cellular proliferation, cellular differentiation, the control of fat metabolism, immune responses, inflammatory responses and the control of glycogen metabolism.
Thus, agents which can modulate (increase or decrease) the activity of serine/threonine kinases have great potential for the treatment of a wide variety of diseases and conditions such as cancer, obesity, autoimmune disorders, inflammation and Type II diabetes.
It has now been found that short peptides which are derivatives of the HJ loop of a serine/threonine kinase can significantly affect the activities of cells expressing the serine/threonine kinase (xe2x80x9cHJ loopxe2x80x9d is defined hereinbelow). For example, the peptide derivatives of the HJ loop of Raf and Polo inhibit the proliferation of bovine aortic cells and the transformed mouse cell lines MS1 and/or SVR cells in vitro at concentrations as low as 10 xcexcM (Example 2). Based on the aforementioned discoveries, novel peptides are disclosed herein which are peptide derivatives of the HJ loop of serine/threonine kinases. Also disclosed are methods of identifying a peptide derivative of an HJ loop of a serine/threonine kinase which modulates the activity of said serine/threonine kinase. Methods of modulating the activity of a serine/threonine kinase in a subject are also disclosed.
One embodiment of the present invention is a novel peptide which is a peptide derivative of the HJ loop of a serine/threonine kinase. The peptide comprises between about five and about twenty amino acid residues or amino acid residue analogs and modulates the activity of the serine/threonine kinase. The N-terminus and/or C-terminus of the peptide can be substituted or unsubstituted. The peptide can be linear or cyclic.
Another embodiment of the present invention is a method of modulating the activity of a serine/threonine kinase in a subject. The method comprises administering a therapeutically effective amount of a peptide which is a derivative of an HJ loop of said serine/threonine kinase, as described above.
Yet another embodiment of the present invention is a method of identifying a peptide which modulates the activity of a serine/threonine kinase. The method comprises providing a xe2x80x9ctest peptidexe2x80x9d which has from about five to about twenty amino acids or amino acid analogs and which is a peptide derivative of the HJ loop of said serine/threonine kinase. The test peptide is incubated with cells having a cellular activity or function under the control of said serine/threonine kinase under conditions suitable for assessing the activity of the serine/threonine kinase. The activity of the serine/threonine kinase is assessed and compared with cells of the same cell type grown under the same conditions in the absence of the test peptide. A greater or lesser activity compared with cells grown in the absence of the test peptide indicates that the test peptide modulates activity of the serine/threonine kinase.
The peptides of the present invention can be used in the treatment of a wide variety of diseases caused by overactivity and underactivity of a STK. Examples include, but are not limited to, cancer, diabetes, obesity, diseases of the central nervous system, inflammatory disorders, autoimmune diseases and cardiovascular diseases. The peptides of the present invention also have in vitro utilities, for example, in the generation of antibodies which specifically bind the serine/threonine kinase from which the peptide was derived. These antibodies can be used to identify cells expressing the serine/threonine kinase and to study the intracellular distribution of the serine/threonine kinase. In addition, the peptides of the present invention can be used to identity and quantitate ligands which bind the NJ loop of the serine/threonine kinase from which the peptide was derived.